The reason ombudsmen matter isn't the direct way their reporting may serve the public, although some do. It's in the way their existence signals an acknowledgement that accountability is right there, at the core of news culture.
The Washington Post is a highly respected newspaper with a wide readership, and should distance itself from base attempts to smear an entire community using misinformation and sensationalism. It should set an example and hold Jennifer Rubin accountable.
The public is being poorly served by the Post's decision. The ombudsman's job is important because it implicitly signals that a major news organization recognizes its power and wants to construct an internal check on the exercise of that power.